Fluorescent coating method



March 3, 1936 C. P. MARSDEN FLUORESCENT COATING METHOD Filed Nov. 21,1933 INVENTOR BY /-M- ATTORNEY Patented Mar. 3, 1 936 UNITED STATESFLUORESCENT COATING METHOD Charles P. Marsden, Bloomfield, N. J.,assignor to Hyg'rade Sylvania Corporation, Salem, Mass, a corporation ofMassachusetts Application November 21, 1933," Serial No. 698,945

5 Claims. (Ci. 91-68) This invention relates to coating methods and withparticularity to coating with fluorescent material.

An object of the invention is to provide a novel method of applying afluorescent coating to glass or other similar support.

A further object is to provide a novel method of applying a fluorescentcoating to a cathode ray tube or similar device.

A feature of the invention relates to a cathode ray tube or similardevice having a fluorescent coating which has a maximum uniformity.

A further feature relates to the method of attaching the fluorescentcoating to the glass or other similar body.

Other features and advantages not specifically enumerated will beapparent after a consideration of the following detailed description andappended claims.

While the invention finds its greatest practical advantages in themanufacture of so-called cathode ray tubes or Braun tubes, the inventivemethod is not limited to the manufacture of any particular kind of tube,but is capable of application in any situation where a uniform coatingof fluorescent material is to be applied to a supporting member.

In certain types of apparatus, for example cathode ray tubes, Brauntubes, or the like, there is provided a screen which comprises amaterial that fluoresces or emits light when bombarded by cathode raysor the like. For example, in one known type of construction employed forthis purpose, the tube is'provided with a constricted or neck portion atone end and an enlarged, substantially flat screen portion at theopposite end, the interior face of this screen portion being providedwith this fluorescent coating. Suitable electrodes are provided withinthe tube for gen-- erating, accelerating and oscillating the beam ofcathode rays which, upon striking the screen, causes the latter tofluoresce or otherwise emit light rays. Such tubes are customarily usedas oscillographs for wave analysis, frequency analysis, etc. Tubes ofthis general type have also been employed for television or picturetransmission purposes, in which case the beam or cathode my not only hasits spacial position varied in synchronism with a transmitter, but alsothe intensity and/or velocity and/or width of the impinging beam arevaried to correspondingly vary the intensity of the fluorescent effectfrom the screen. While, for oscillograph or similar uses it is importantthat the fluorescent coating be uniform, minor variations of thicknessor uniformity of the grain in the coating do not seriously affectresults. However, in television or similar uses it is absolutelynecessary, if truly faithful images are to be reproduced, that thefluorescent coating be not only of the highest uniformity as tothickness, but it is also important that the individual grainsconstituting the coating be, as far as possible, of the same degree offineness. It is further highly important in all types of cathode raytubes that the fluorescent 10 coating be firmly united to the glass orother support, since it is required to be bombarded continuously by thecathode rays.

Various methods have heretofore been proposed for applying thefluorescent coating. For exam- 15 pie, the most common way is to mix thefluorescent coating with a suitable binder which is then sprayed overthe surface to be coated. Needless to say, with ordinary sprayingmethods it is extremely dificult to secure a coating of uniformthickness. 'Ihis may be due to a variety of causes. For example, inspraying it is required that the material be sprayed onto the receivingsurface at substantially right angles, with the result that if anon-uniform or large grain of materialattaches itself to the supportingsurface, succeeding traverses of the spray aggravate and accentuate thethickness of the coating at this point. Added to this is the fact thatii the coating is not evenly united to the support over its entiresurface, the force of the spray may dislodge one or more grains from thecoating. Other methods such as painting or the like obviously areincapable of producing uniform coats because of the appreciable physicaldimensions of the painting tool as compared with the fine grainconstituting the coating.

It has been found that a thoroughly uniform fluorescent coating may beachieved in accordance with this invention without spray, painting 40 orsimilar processes.

In accordance with the invention the surface of the tube to be coated isfirst provided witha tenuous film of tacky or sticky material or amaterial which exhibits pronounced adhesive properties for the powderedfluorescent material. This fluorescent material is preferably employedin powdered form and preferably mixed with another powdered weightymaterial such as powdered zinc or the like. The powdered mixture is thenpoured or deposited in any familiar manner upon the same flim to whichit adheres. The support is then rotated, oscillated and/or swirled so asto agitate the powdered mixture relative to the said fllm, thusdistributing the fluorescent powdered material in an even deposit overthe fllm. The excess of powdered material may thenberemovedbypouringorsimiiarprocess, after which thesupportmaybeheatedbakedorflred toaduilredheattoremovethefllmand/orbinders, resulting in a flrm attachment of the fluorescent material ontothe glass or other nipport.

while the foregoing description gives a general plan of the preferredprocedure to be employed, a detailed description will now be given ofthe manner of practicing the invention in connection with a typical formof cathode ray tube.

Referringtothedrawing,themunerallindicates generally a glass or othertube having a constricted or neck portion 2 and a flared or enlargedportion 3. The portion 3 terminates in a substantially flat portion Awhich serves to carry the fluorescent material. In accordance withwell-known practice in the art of cathode ray tube design, the tube l isprovided with an emitting cathode represented schematically by thenumeral 5, and an electrode or electrodes 6 for varying the intensity ofthe cathode ray beam.

A concentrating or focusing electrode 1 is usually provided to restrictthe beam to a comparatively narrow width. A pair of vertical deflectingplates 8 and a pair of horizontal deflecting plates 9 (one shown).areprovided for oscillating the cathode ray beam over any predeterminedpath. A suitable anode or anodes II are provided for accelerating theelectrons from the cathode i. The manner of producing and oscillatingthe cathode ray beam. above described constitutes no feature of thepresent invention and any wellknown means may be provided for thispurpose.

Prior to attaching the constricted or neck portion 2 to the flaredportion i, the latter flared portion 3 has the interiorsuri'ace of thewall I provided with a tenuous fllm preferably of the nature of aplasticized lacquer indicated in the drawing by the numeral II. It ispreferred to employ a binder consisting of, for example, a solution ofnitro cellulose in a volatile solvent, e. g., ethyl carbonate, amylacetate, etc. This binder solution is then plasticized preferably bymixing with it dibutyl phthalate, and in order to retard the drying, asmall percentage, such as 1% of diethyl oxalate may be mixed with thebinder. It is to be understood, of course, that the invention is notlimited to this particular plasticizing agent. For example, any diamylor diethyl phthalate or phthalates may be employed or, if desired,dicresyl phosphate my be employed. The invention also contemplates theuse of lacquer fllms containing gums, if these lattergumsareburntoutintheflnalflring. As above stated, the plasticized fllm is preferablyof a tenuous character or sufliciently thin so as to be substantiallycompletely transparent, although it will be understood that any otherknown transparent fllm may be employed which, upon flring, iscompletely-removed or becomes transparent.

The fllm is preferably deposited by pouring or other similar operation.For example, if the portion 4 of the tube is five inches in diameter,approximately 2 cc. of the above material may be dropped on the interiorface of the portion I and allowed to flow evenly over the surface. Anyexcessofthematerial overtherequiredamount may be drained of! in anysuitable manner, with the result that there is produced a tenuom uniformfllm which is substantially free from bubbles, flowing marks. etc.Thisfllmisthen allowed todryoritsdriedtothepointwhereiteomesappreciabiytackyorstickmandtheelcess,

fluorescent material. Any well-known fluorescent material such asordinarily employed in cathode ray tubes or the like my be employed.Preferably this material is intimately mixed with a weighty powderedzinc of about 30 mesh. The mixed powdered materials are then pom-ed intothe bulb and the bulb is swirled, oscillated, and somewhat violentlyshaken so as to distribute the relatively flne fluorescent material inan even depositoverthestickyflhn Ii. Asaruultoftbis agitating processthe heavy grains or particles of zinc or other weighty material causethe powdered fluorescent material to be distributed in a uniform layerover the fllm ll. One posible explanation for this is that the very flneparticles of the fluorescent material are held by a sufiicient adhesiveforce to prevent their dislodgment by the moving or swirling weightyparticles of zinc, whereas the non-uniform or enlarged grains of thefluorescent material are carried by the swirling or agitated weightymaterial, with the result that the fluorescent coat which flnallyadherestothefllm ll consistsofsubstantiallylmiform and finely grainedfluorescent material. The excess of the powdered materials may then bepoured out .or otherwise removed from the tube. If, upon examination ofthe tube, it is discovered that there is an excess of fluorescentmaterial forming a lump at any particular portionofthefllm,thiscanberemovedbyaddingmore zinc orsimilarweightymaterialandcontinuing the swirling action until the lump or non-uniformity isremoved. The material having thus been removed, the edges of the coatingmay be trimmedbyrotatingthebulbandwipingoii'the material with a cloth orrubber scraper.

'iheendlofthetubeisthensubiectedtoheat,preferablytoraiseittoadullredheatortoa temperature at which the binderand/or the plasticized fllm ii is removed. Preferably also, the heat ismaintained for a suflicient length oftimetotakethefluorescentmaterialontothe member I.

Aimbepreparedinaccordancewiththeabove coatinghasbeenfound toextremelyuniform graining and thickness of fluorescent materialanditwili be obviouaofcourse, that variuaily increased until the fllm isentirely removed.

If desired, the above procedure may be repeated so as to provide vecoats of fluorescent material, each coating having a thick nesspractically consisting of a single grain.

The portion {thus prepared may then beunitedorsealedtotheneckportioniandthe tubemaythenbesubiectedtotheo'evacuation and treatment customarily employed in the manui'actin'e ofvacuum tube and electron tube devices in general.

lthasbeenfoimdthattheformingmethodzg renders it possible to vary thethickness of the fluorescent coating from an almost transparent deryfluorescent material containing fine and coarse grains to a cathode raytube which comprises, flowing onto said support a smooth thin fllm of aplasticized lacquer binder solution, drying said film until the odor ofthe solvents is substantially entirely removed and said film becomesappreciably tacky, depositing said powdery material on said fllm, andswirling said support to cause the coarser grains of said material todistribute the finer grains of said material in a uniform layer on saidfilm, removing any excess of said material, and heating the support toremove excess lacquer and to bake said powdery material on said support.

2. The method of providing a cathode ray tube with a uniform coating ofpowdery fluorescent material which comprises, flowing onto a wall ofsaid tube a thin fllm of a plasticized binder solution, drying saidsolution to the point where it becomes appreciably tacky and the odor ofthe solvents is substantially entirely removed, mixing with the powderyfluorescent material another powdery material of greater weight than thefluorescent material, depositing said mixture on said flim, swirling andshaking said tube to distribute said fluorescent material in asubstantially uniform layer, removing any excess of said mixture, andheating the wall of said tube to bake said powdery material thereon.

3. The method of applying a uniform coating of fluorescent material to acathode ray tube which comprises, flowing onto a wall of said tube athin film of a transparent plasticized lacquer, mixing with the powderyfluorescent material a quantity of powdery material which is heavierthan the powdery fluorescent material, depositing said mixture on saidfilm while said fllm is appreciably sticky, swirling and shaking saidmixture until lighter grains are distributed in a uniform layer oversaid film, removing excess of said mixture, and heating the wall of thetube to bake the powdery material thereon.

4. The method of providing a cathode ray tube with a fluorescent coatingwhich comprises, mixing a phthalate with a nitrocellulose binder, de-

positing said mixture in a thin film onto a wall.

of said tube, drying said fllm until the solvents are substantiallyentirely removed, mixing with Y the fluorescent material anotherweightier powdered material, swirling the tube to cause the weightiermaterial to distribute the grains of the fluorescent material uniformlyover said film, and subsequently heating said fllm to remove saidbinder.

5. The method according to claim 4 in which the fluorescent material ismixed with a powdered zinc of approximately mesh.

CHARLES P. uansmm.

